An MGLMultiPolygon object represents a shape consisting of one or more
polygons that do not overlap. For example, you could use a multipolygon shape
to represent the body of land that consists of an island surrounded by an
atoll: the inner island would be one MGLPolygon object, while the surrounding
atoll would be another. You could also use a multipolygon shape to represent a
group of disconnected but related buildings.